feat: implementing http_file_curl and test

[lnpotter]

• The http_file_curl enables users to perform asynchronous file downloads using the cURL command. It constructs a curl command based on the specified HTTP method and URL, allowing the request to run in the background.
• The unit test for the http_file_curl with a GET request verifies that the function correctly initiates a file download using the GET method. It simulates a response from the cURL command and checks if the returned status and body match the expected values.

This PR covers #54